如何通过BLE传输数据？

Question

I am currently evaluating the board of Maxim Integrated MAXREFDES100# . As part of my thesis, I would like to examine whether there is the possibility of using BLE for data streaming.

The supplied software is fully functional and can already transfer data. Of course, only smaller data packets over a longer period like Temperature or precalculated Heart Rate values. I am aware that BLE is not suitable and has not been designed to transmit data continuously. Nevertheless, I would like to try to transfer the ECG raw data also via the BLE interface. So that I can check whether my data has been arrived completely and correctly in time (prerequisite for ECG data), I have developed the following test setup:

Currently, I store data of a sine wave to a large FIFO and transfer 20-byte sine packets to a characteristic. So far everything works wonderfully. Using an Android device and a BLE sniffer I catch the data packets and check if the sine has any interruptions. The following graphic is taken from a longer measurement: (I have tested my FIFO and the sine datas are complete without any inerruption): This is a capture of my Android and my BLE Sniffer: Data packets are missing.

Sine & Spektrogram Image

Further measurements show that the errors do not occur sequentially, they can always be found at different times. (The Fifo Implementation must be correct)

Sine & Spektrogram Image 2

Since my phone and my Adafruit BLE sniffer have identical errors in the same place, the data packages on the board-side must be corrupt. I suspect they are lost at some protocol level (GAP maybe?). Interestingly, errors affect at least 200 following bytes (256 bytes data are a complete sine). This means that at least 10 data packets each 20 Bytes would have to be in order to get such a graphic.

• What options are there for continuously sending data via the BLE interface?
• Is it possible to send the data directly via L2CAP without GATT/ATT?
• Are there any more wireless, low power protocols that allow data streaming? (So ​​with acknowledgment like TCP for completeness and chronological correctness)

Best regards, Emin

Answer 1

• What options are there for continuously sending data via the BLE interface?
• Is it possible to send the data directly via L2CAP without GATT/ATT?

BLE v4.1 introduced LE Connection-Oriented Channels which is a way to send data directly via L2CAP without GATT/ATT (think about network sockets). See also Bluetooth Core Specification Vol. 3 Part A Section 3.4.

The board you are using has a EM9301 BLE chip which seems to support BLE v4.1. However, the mbed library you are using doesn't allow you to use them. See here , you have an interface for connect/disconnect callbacks and GATT characteristics read/write/notification. Nothing about LE Connection-Oriented Channel.